In the prior art, there has been known an image generating system for generating an image which can be seen from a given view point in an object space or a virtual three-dimensional space. This image generating system is highly popular because it allows the so-called “virtual reality” to be experienced. In the image generating system capable of enjoying the racing game, for example, the player enjoys the three-dimensional game by manipulating a racing car (or object) to run in the object space so that the car may compete with another racing car manipulated by another player or a computer.
In this image generating system, it is an important technical target for improving the virtual reality of the player to generate a more real image.
Generally in the image generation, the polygon coordinates existing in the three-dimensional space are perspectively projected and transformed into a screen coordinate system and are then written in a frame buffer. At this time, in the case of a vertex of a polygon existing on a screen end at a short distance from the viewpoint, the Z-value is approximate 0 so that the perspectively transformed value exceeds a predetermined range. As a result, the polygon is not written in the frame buffer to cause a trouble that the image is formed to have the polygon omitted. If the polygon is especially large, there arises a problem that the display failure is conspicuous.
As one method for eliminating this problem, there is a method for reducing or making the display failure inconspicuous by dividing the polygon into a plurality of smaller polygons. However, this method is troubled by a problem that the vertex, as should be located at the same position after the division, is shifted at the time of interpolating two vertex coordinates to generate a gap.